Best way to cut holes for HVAC supplies in lathe and plsster

[Andrew R.]

I need to cut 10 holes for my sub, what's the best way to not have damage outside the cut?

[David Meiland]

Round holes?

[Andrew R.]

Rectangles

[tjbnwi]

I'm not sure what plsster is?????????? (kidding)

Multi Master would be slow, but most accurate. They have a diamond blade. RotoZip with diamond or carbide bit. RotoZip with saw attachment and tile blade.

Tom

[David Meiland]

I'm not a rotozip expert, but I wonder if there's a way to use a template and maybe a carbide bit to cut them out, or at least get all the way through the plaster. Another option would be a small circular saw and a blade that's going to get thrown out, since the holes are rectangles.

[tjbnwi]

I would figure an "inside" template, smaller by the "shoe" to bit outside distance, secure it to the plaster/lath where needed, run the shoe along the template counter clockwise. With the RotoZip turned on of course. You may need to drill a pilot hole. Have someone shadow the bit with a vacuum hose, attached to your hepa vac with the vac turned on of course.

Tom

[Andrew R.]

I'm not sure what plsster is?????????? (kidding)

Multi Master would be slow, but most accurate. They have a diamond blade. RotoZip with diamond or carbide bit. RotoZip with saw attachment and tile blade.

Tom

I do have an MM and I have a plaster blade. I fear the blade hitting the wood lathe and vibrating plaster loose yes/no?

[tjbnwi]

As long as the lath is solidly nailed I do not think it should be an issue. Once through the plaster change blades.

Tom

[calvert]

Andrew, If plaster is sanded basecoat use a diamond wheel in a grinder with the vac. trailing. After cutting through the plaster finish and basecoat remove the material from the wood lath with a small prybar or stiff putty knife. Then I would use a cordless circ. saw to cut the lath .. you know, something with a 6" or smaller blade. This would create the least vibration on the rest of the plaster and give the cleanest hole.

Or, just do like most electricians and plumbers do on any plaster jobs I go to and take out your hammer and bash a hole in the wall.

[NW Architect]

If at first you don't succeed, on the second hole, cut it twice.
First cut a 6x6 opening in two passes, first through the plaster, then through the lath. Then shove a couple of 5x10 pieces into the opening and clamp them off to brace the back of the lath (bolts pre installed on the pieces, then a 1x2 across the front). Cut to your 10x10 line after all that.

[m beezo]

One thing I would consider is making sure the client knows there is a possiblitly of damage no matter how you cut it out. I work with a lot of lath and plaster and all the ideas that have been talked about have worked for me. However there is an awful lot of flex in the wood lath if your hole is right in the middle of the stud bay. The good thing is that by cutting a 10 inch hole you are going to be pretty close to the studs on each end so the amount of flex should be cut down quite a bit.

One thing I have done is push the plaster out of the void between the lath with a small screw driver just enough to get a homemade flat hook tool in there. I then use that to steady the lath and cut with my multi tool. That helps keep the lath from shaking . By also removing the plaster it helps my wood cutting blades last a little longer. I have also used the flat super bars from time to time but they are almost too thick to get in between the lath sometimes.

Never rush the job and be prepared for the one that the lath moves enough to crack the plaster. I might get lucky and do all my cuts but there is somedays there is one that cracks the plaster. I wish I knew what I was doing differently but can not put my finger on what the problem was but it cracked.

[Happy Home]

I've drilled 1" holes in the corners and used a Sawzall. Worked well.

Given what I've read here I'd do the same except with a outside template to allow for the Sawzall shoe and shaving cream on the cut line to keep the dust down.

[kfc510]

If you have reason to expect the plaster is prone to separating and/or cracking, I'd consider screwing some boards to the studs on either side to hold it all together. Line them up with the edges of the studs, then sister some nailers on to the studs to accept the patch after you're done.

Here's some pics of a ceiling demo where we did that at the joist.

[kfc510]

Next two pics.

[kfc510]

With nailer sistered at appropriate depth.